1. Field of the Invention
The present invention relates to a process for purifying silicon source materials, and more particularly to a process for purifying trichlorosilane or mixtures of trichlorosilane and silicon tetrachloride by high gravity rotating packed bed.
2. Description of Relative Prior Art
Electronic grade polysilicon (EGS) can be obtained from trichlorosilane or mixtures of trichlorosilane and silicon tetrachloride after removing impurities such as boron and phosphorus. Most impurities can be readily removed from trichlorosilane or silicon tetrachloride by distillation. Trace impurities of boron or phosphorus which are usually present in the form of BCl3, PCl3, B2H6 or PH3, however, to reduce such contamination to an acceptably low level by distillation would require several sequential distillation steps. One reason is that the bubble of the impurity gases is not easy to pump out from the liquid state of trichlorosilane and silicon tetrachloride, and the impurity gas may dissolve in the liquid. The other reason is that the boiling point of BCl3 (12.5° C.) and PCl3 (74.2° C.) is not high enough nor low enough and may coming out with trichlorosilane when the temperature rise above 32° C. to extract trichlorosilane.
U.S. Pat. No. 5,616,245 to Albrecht et al. teaches a high gravity separator to separate solid materials. Other process has been proposed for purifying water to remove out the oxygen or other gas with a high gravity separator. U.S. Pat. No. 4,283,255 to Ramshaw et al. teaches a process and apparatus for effecting mass transfer between two fluid phases by using a rotating element, but none of the prior arts using rotating element is used to remove the impurities in silicon source materials. U.S. Pat. Nos. 4,374,110 and 4,409,195 to Darnell et al. teaches a process to purify silicon source materials by reacting small amounts of oxygen with trichlorosilane in gas state at a temperature between 170° C. or 60° C. to 300° C.
It is desirable to have a purification process which achieve a still higher level of purification and does not require the time and expense of multiple distillation and high temperature reaction.